Studies of enhanced edge emission of a large area cathode

Electra is a repetitively pulsed, electron beam pumped krypton fluoride (KrF) laser that will be used to develop the technology required for inertial fusion energy (IFE). A full scale fusion KrF laser will be pumped with electron beams with cross-sections of 2,500 to 10,000 cm/sup 2/. Understanding the mechanisms that govern uniform electron beam emission over such large areas is important for the overall system efficiency and durability. This paper presents measurements of the current density along the edge of a large area electron beam. The spatial and temporal current density data is obtained with a Faraday cup array at the anode, and the spatial time-integrated current density is obtained with radiachromic film. MAGIC particle-in-cell (PIC) simulations support the experimental results. Experiments and simulations showed that recessing the cathode minimizes the electric field at the edge and eliminates the edge effect.